AMERICA’S FIRST CORPS of astronauts, known as the Mercury Seven, had it pretty rough back in 1959. Selected from hundreds of elite pilots, they had to endure a battery of grueling tests: running on treadmills for hours, blowing up balloons repeatedly to gauge their lung capacity, being exposed to extreme heat, vibration and loud noises. None could weigh over 180 pounds or be taller than 5-foot-11. And they needed to have logged at least 1,500 hours of flying time in a traditional aircraft.

The bar has since lowered drastically, especially for ordinary citizens hoping to catch a ride aboard the commercial “space-tourism” flights that have either launched or have plans to do so as soon as early next year. Just ask the 700 ticket holders who’ve paid up to $250,000 to ride with Virgin Galactic 50 miles above the earth, or the 300 who have signed up for a similar offering by XCOR (at a cost of $95,000). Overweight? Probably not a problem. Heavy smoker? The sky may still be the limit. Even if you think you haven’t got the right stuff, you might. It could just take a bit of training to get you there.

Interactive: Ticket to Ride

Surprisingly, the baseline medical requirements for commercial space travel are lenient—and that’s true whether you’re taking a “suborbital” flight that barely leaves the earth’s atmosphere (as Virgin Galactic and XCOR’s flights will do) or going all the way to the International Space Station (a trip offered by a company called Space Adventures).

According to a Virgin Galactic spokesperson, the “vast majority” of the general population will be able to fly with the company, even those with “heart disease, diabetes, high blood pressure, joint replacements, lung disease and other conditions,” assuming proper precautions are taken. XCOR participants must pass a basic physical exam, like that required to acquire a pilot’s license, but the company welcomes all, as long as passengers fit in the seat and can open the spacecraft door in case of an emergency on the ascent or descent. (You also can’t be heavier than 250 pounds if you want the XCOR spacecraft to reach its maximum altitude of 100 km) And although the FAA requires that commercial spaceflight participants be 18 or older, neither service has a maximum age limit. Virgin Galactic has provisionally cleared customers in their 80s.

The much more involved Space Adventures’ Orbital Spaceflight program, which lets civilians hitch a ride aboard the Russian Soyuz to spend 10 to 14 days in the International Space Station, is equally inclusive in its approach. Although passengers are screened for health issues that would be difficult to treat in space, “most people in good health will qualify for spaceflight,” said Space Adventures president Tom Shelley. And there is a precedent for civilians making it safely to space and back again. The company took its first passenger, Dennis Tito, then 61, up to the space station back in 2001. Seven others have since then, including Guy Laliberté, founder of Cirque du Soleil. British soprano Sarah Brightman, next in line, is scheduled to go up next year.

Besides Space Adventures, Virgin Galactic and XCOR are the other main ventures focused specifically on taking passengers to space. ( Elon Musk ’s SpaceX and Jeff Bezos ’s Blue Origin are concentrating on commercial payloads). Virgin Galactic has done test flights and plans to take passengers up in 2015. XCOR says its test flights will begin early next year, with passengers going up as soon as next winter.

Space travel is not for the faint of heart, however. Even during relatively short suborbital trips, your body is subjected to extremes during ascent and re-entry. The rate of acceleration can cause blackouts, because the blood rushing from your head to your feet makes the heart pump faster to keep you conscious. On re-entry, the Virgin Galactic flight briefly hits 6 gs—or six times the earth’s gravity. (XCOR’s flight tops out at 4 gs.)

All three services provide guidance on how to mitigate this. When passengers buy a ticket with Virgin Galactic or XCOR, they’re put in touch with a trainer. Richard Searfoss, a former NASA astronaut and retired Air Force Colonel who now serves as XCOR’s staff trainer, suggests doing abdominal exercises so passengers will be better able to engage their core on re-entry. Passengers are taught “straining maneuvers”—a technique that involves tensing your muscles to help keep blood in the chest area, so it can get pumped up to the brain. He also recommends doing cardio exercises to ensure that you don’t have trouble breathing under the g loads.

And then there are simple movements—like maneuvering around the spacecraft cabin—that most people aren’t accustomed to. “You’re crouching to climb into the spaceship and stretching to get out of your seat and doing new motions that you normally don’t do in regular terrestrial life,” said Beth Moses, who was once the International Space Station assembly manager and is now Virgin Galactic’s chief astronaut trainer. She advises future passengers to stretch regularly before the flight.

Both Virgin Galactic and XCOR’s ticket price includes three days of training, during which passengers take an aerobatic flight that will subject them to g-forces similar to those they’ll experience in the spacecraft. Both companies recommend future passengers ride in a centrifuge flight simulator in advance to get a sense of how the heightened forces will feel.

Space Adventures’ much more involved Orbital Spaceflight program has a rigorous training program to match. Passengers spend roughly six months embedded with astronauts in the Russian Federal Space Agency at the Gagarin Research & Test cosmonaut Training Center in Star City, Russia.

Esther Dyson, an entrepreneur and investor in a handful of space-tourism companies including XCOR and Space Adventures, elected to be a “backup cosmonaut” (current cost: $4 million). In addition to daily classes on “space plumbing” and “space medicine,” she recalled spending two nights in the snowy woods—an exercise meant to prepare her for an emergency landing in winter. She and two other cosmonauts had to pitch a makeshift tent and build a fire, using only an ax and the silk from their parachutes.

Ultimately, the physical preparation is as much about comfort as it is about survival. “We’ve been doing a lot of work to demonstrate that physical fitness is not a necessity,” said Dr. Rebecca Blue, a flight surgeon currently employed by Virgin Galactic. Dr. Blue, as an assistant professor at the University of Texas Medical Branch at Galveston, led a study independent of Virgin Galactic that found even people with common medical problems—including asthma, emphysema and back and neck injuries—could safely withstand the stress of commercial space travel. “We want people to take this opportunity to really kind of focus on health and fitness as a lifestyle choice, so you enjoy the flight and don’t simply tolerate it.”

Stellar Staycations

Don’t have $95,000 to blow on a ticket to space? Here are four ways to get an out-of-this-world experience here on earth

Take a Spin in a Centrifuge. To get a taste of the 4 to 6 gs that you’d experience during a spaceflight, ride in the Phoenix Centrifuge, at the National Aerospace Training and Research Center, in Southampton, Penn. It’s a 25-foot rotating arm with a space-cabin cockpit attached to the end. The NASTAR Center offers a two-day foundational course in suborbital spaceflight, which includes skills training and time in the centrifuge, for $3,000. nastarcenter.com

Lose Some Weight. You don’t have to travel to space to experience weightlessness. Zero Gravity Corporation offers weightless flights in a modified Boeing 727 that is flown in a series of parabolic paths. As the plane makes its way over the top of the parabola, passengers experience weightlessness for 20- to 30-second intervals. Each excursion includes 15 of these maneuvers. Flights cost $4,950 and depart from locations throughout the U.S., including Cape Canaveral and Ft. Lauderdale, Fla.; Las Vegas, Nev.; and San Jose, Calif. gozerog.com

Go to Basic Training. The U.S. Space & Rocket Center’s Adult Space Academy, in Huntsville, Ala., offers a number of ways to experience the rigors of space travel. A flight simulator, built inside a mock-up of the cockpit of the space shuttle, gives you the experience of commandeering a spacecraft, while the 1/6th Gravity Chair is basically a spring-loaded seat, suspended from the ceiling, that gives you the feeling of bouncing along the moon. There’s also a Multi-Axis Trainer that spins the sitter in various directions to mimic the “tumble spin” an astronaut might experience during reentry in a space capsule. The Academy costs $499 for a three-day program, $599 for four. spacecamp.com

Ride a 4-G Roller Coaster. Although even the fastest roller coasters don’t subject the body to the pressure an astronaut experiences, you can get a 4-g experience at some amusement parks. Try Batman: The Ride, at Six Flags Fiesta Texas in San Antonio (sixflags.com), to name just one.

Corrections & Amplifications
Virgin Galactic flights will reach a maximum altitude of 100 km. An earlier version of a chart with this article said the height was 80 km.